Cooled turbine ring segments with intermediate pressure plenums

ABSTRACT

A ring segment for a gas turbine engine includes a panel and a cooling system. The cooling system is provided within the panel and includes an elongated intermediate plenum extending parallel to leading and trailing edges of the ring segment, and is located radially between an inner side of the panel and a hook structure extending from an outer side of the panel. A plurality of cooling fluid feed passages supply cooling fluid to the intermediate plenum, and a plurality of convective cooling passages extend through the panel from the intermediate plenum to one of the leading and trailing edges for cooling the inner side of the panel. The intermediate plenum is located in axial alignment with and defines an area of reduced thermal mass receiving impingement cooling adjacent to the hook structure.

CROSS REFERENCE TO RELATED APPLICATION

This application claims the benefit of U.S. Provisional Patent Application Ser. No. 61/592,102, filed Jan. 30, 2012, entitled “IMPINGEMENT CONCEPT WITH INTERMEDIATE PRESSURE PLENUMS FOR COOLED TURBINE RING SEGMENTS”, the entire disclosure of which is incorporated by reference herein.

FIELD OF THE INVENTION

The present invention relates to ring segments for gas turbine engines and, more particularly, to cooling of ring segments in gas turbine engines.

BACKGROUND OF THE INVENTION

It is known that the maximum power output of a combustion turbine is achieved by heating the gas flowing through the combustion section to as high a temperature as is feasible. The hot gas, however, heats the various turbine components, such as airfoils and ring segments, which it passes when flowing through the turbine section. One aspect limiting the ability to increase the combustion firing temperature is the ability of the turbine components to withstand increased temperatures. Consequently, various cooling methods have been developed to cool turbine hot parts.

In the case of ring segments, ring segments typically may include an impingement plate, associated with the ring segment and defining a plenum between the impingement plate and the ring segment. The impingement plate may include holes for passage of cooling fluid into the plenum, wherein cooling fluid passing through the holes in the impingement plate may impinge on the outer surface of the ring segment to provide impingement cooling to the ring segment. In addition, further cooling structure, such as internal cooling passages, may be formed in the ring segment to facilitate cooling thereof.

SUMMARY OF THE INVENTION

In accordance with an aspect of the invention, a ring segment for a gas turbine engine is provided. The ring segment includes a panel comprising a plurality of side edges including leading and trailing edges extending in a circumferential direction, and first and second mating edges extending in an axial direction. The panel further comprises an outer side and an inner side, wherein cooling fluid is provided to the outer side, and the inner side defines at least a portion of a hot gas flow path through the gas turbine engine. The panel also includes a central recessed portion defining a recessed surface formed in the outer side and surrounded by a rim portion comprising an unrecessed portion extending around an outer periphery of the recessed portion along each of the side edges. A front hook structure extends in a radial direction from the rim portion at a leading edge side of the recessed portion, and a rear hook structure extends in a radial direction from the rim portion at a trailing edge side of the recessed portion. A cooling system within the panel receives cooling fluid from the outer side of the panel for cooling the panel. The cooling system comprises an elongated intermediate plenum extending in the circumferential direction and located radially between the inner side of the panel and one of the front and rear support structures. A plurality of cooling fluid feed passages extend from the recessed portion to the intermediate plenum for supplying cooling fluid to the intermediate plenum. A plurality of convective cooling passages extend through the panel from the intermediate plenum to one of the leading and trailing edges for cooling the inner side of the panel. The intermediate plenum is located in axial alignment with the one of the front and rear support structures and defines an area of reduced thermal mass adjacent to a radially inner end of the one of the front and rear support structures.

The cooling fluid feed passages may provide impingement cooling to the intermediate plenum. A cooling fluid pressure drop through the feed passages is typically less than a cooling fluid pressure drop through the convective cooling passages. A passage diameter of the convective cooling passages may be less than a diameter of the cooling fluid feed passages, and the intermediate plenum may define a diameter greater than both the convective cooling passage diameter and the diameter of the cooling fluid feed passages.

Fluid supply ends of the convective cooling passages may be located at the intermediate plenum and the fluid supply ends may be axially aligned with at least a portion of the one of the front and rear support structures.

The cooling structure may further include an elongated axial plenum structure extending in the axial direction, a plurality of cooling fluid feed passages extending from the recessed portion to the axial plenum structure for supplying cooling fluid to the axial plenum structure, and a plurality of exit passages extending from the axial plenum structure to at least one of the first and second mating edges. The axial plenum structure may comprise a forward plenum and a rearward plenum, and cooling fluid may be supplied to the forward plenum at a different flow rate than cooling fluid supplied to the rearward plenum. The axial plenum structure may also include first and second axial plenum structures extending in the axial direction adjacent to the first and second mating edges, respectively, and the intermediate plenum may include opposing ends located adjacent to the first and second axial plenum structures.

The convective cooling passages may extend generally parallel to the inner side of the panel and may be defined by a passage diameter, and the convective cooling passages may be spaced within a distance of about one passage diameter from the inner side of the panel. The passage diameter of the convective cooling passages may be less than a diameter of the cooling fluid feed passages.

The intermediate plenum may comprise a first intermediate plenum located in axial alignment with the front hook structure, and the cooling system may further include a second elongated intermediate plenum extending in the circumferential direction and located in axial alignment with the rear hook structure, a plurality of cooling fluid feed passages extending from the recessed portion to the second intermediate plenum for supplying cooling fluid to the second intermediate plenum, and a plurality of convective cooling passages extending through the panel from the second intermediate plenum to the trailing edge for cooling the inner side of the panel.

In accordance with another aspect of the invention, a ring segment for a gas turbine engine is provided. The ring segment includes a panel comprising a plurality of side edges including leading and trailing edges extending in a circumferential direction, and first and second mating edges extending in an axial direction. The panel further comprises an outer side and an inner side, wherein cooling fluid is provided to the outer side, and the inner side defines at least a portion of a hot gas flow path through the gas turbine engine. Front and rear support structures extend in a radial direction from the outer side of the panel. A cooling system within the panel receives cooling fluid from the outer side of the panel for cooling the panel and comprises first and second elongated intermediate plenums extending in the circumferential direction and located radially between the inner side of the panel and respective ones of the front and rear support structures. A plurality of cooling fluid feed passages extend from the outer side of the panel to the intermediate plenums for supplying cooling fluid to the intermediate plenums. A plurality of convective cooling passages extend through the panel from the first and second intermediate plenums to the leading and trailing edges, respectively, for cooling the inner side of the panel. The first and second intermediate plenums are located in axial alignment with the front and rear support structures, respectively, and define an area of reduced thermal mass adjacent to a radially inner end of each of the front and rear support structures.

The convective cooling passages may define a passage diameter that is less than a diameter of the cooling fluid feed passages, and the first and second intermediate plenums may define a diameter greater than both the passage diameter and the diameter of the cooling fluid feed passages.

Fluid supply ends of the convective cooling passages may be located at the first and second intermediate plenums, and the fluid supply ends may be axially aligned with at least a portion of respective ones of the front and rear support structures.

The cooling structure further may include first and second elongated axial plenum structures extending in the axial direction adjacent to the first and second mating edges, respectively, a plurality of cooling fluid feed passages extending from the outer side of the panel to the axial plenum structures for supplying cooling fluid to the axial plenum structures, and a plurality of exit passages extending from the axial plenum structures to one of the first and second mating edges.

Each of the first and second axial plenum structures may comprise a forward plenum and a rearward plenum, and cooling fluid may be supplied to the forward plenums at a different flow rate than cooling fluid supplied to the rearward plenums.

A fluid connection may be provided between ends of each of the first and second intermediate plenums and the first and second axial plenum structures.

In accordance with a further aspect of the invention, a ring segment is provided for a gas turbine engine. The ring segment includes a panel comprising a plurality of side edges including leading and trailing edges extending in a circumferential direction, and first and second mating edges extending in an axial direction. The panel further comprises an outer side and an inner side, wherein cooling fluid is provided to the outer side, and the inner side defines at least a portion of a hot gas flow path through the gas turbine engine. A cooling system within the panel receives cooling fluid from the outer side of the panel for cooling the panel and comprises an elongated intermediate plenum extending in the circumferential direction and located radially between the inner and outer sides of the panel. A plurality of cooling fluid feed passages extend from the outer side of the panel to the intermediate plenum for supplying cooling fluid to the intermediate plenums. A plurality of convective cooling passages extend through the panel from the intermediate plenum to one of the leading and trailing edges for cooling the inner side of the panel. The convective cooling passages extend axially generally parallel to the inner side of the panel and are defined by a passage diameter, and the convective cooling passages are spaced within a distance of about one passage diameter from the inner side of the panel.

The intermediate plenum may be aligned in the axial direction with a radially inner end of a hook structure that extends in a radial direction outwardly from the outer side of the panel for supporting the panel within the engine, the intermediate plenum effecting an area of reduced thermal mass adjacent to the inner end of the hook structure.

The passage diameter of the convective cooling passages may be less than a diameter of the cooling fluid feed passages, and the intermediate plenum may define a diameter greater than both the convective cooling passage diameter and the diameter of the cooling fluid feed passages.

BRIEF DESCRIPTION OF THE DRAWINGS

While the specification concludes with claims particularly pointing out and distinctly claiming the present invention, it is believed that the present invention will be better understood from the following description in conjunction with the accompanying Drawing Figures, in which like reference numerals identify like elements, and wherein:

FIG. 1 is cross sectional view of a portion of a turbine section of a gas turbine engine, including a ring segment constructed in accordance with the present invention;

FIG. 2 is a perspective view of the ring segment illustrated in FIG. 1;

FIG. 2A is a perspective view illustrating passages of the cooling system of the present invention;

FIG. 3 is a cross sectional view taken along line 3-3 in FIG. 2;

FIG. 3A is an enlarged view of the leading and trailing edge portions shown in FIG. 3; and

FIG. 4 is a cross sectional view taken along line 4-4 in FIG. 2.

DETAILED DESCRIPTION OF THE INVENTION

In the following detailed description of the preferred embodiment, reference is made to the accompanying drawings that form a part hereof, and in which is shown by way of illustration, and not by way of limitation, a specific preferred embodiment in which the invention may be practiced. It is to be understood that other embodiments may be utilized and that changes may be made without departing from the spirit and scope of the present invention.

The present invention provides a ring segment including a panel provided with a cooling system that enables increased cooling effectiveness within the edges of the ring segment and facilitates cooling of an inner segment surface facing the hot gas path. The cooling system includes intermediate plenums of a predetermined size to supply a flow of cooling air through a plurality of convective cooling passages located generally parallel to, and closely adjacent to the inner segment surface. The configuration of the cooling passages provided by the present invention addresses a perceived problem of thermal barrier coating degradation that occurs at the inner surface of the panel, and is believed to be caused by elevated temperatures within the ring segment adjacent to the inner surface that could contribute to spallation of the thermal barrier coating with eventual depletion of the underlying bond coat and exposure of the metal of the panel.

A particular location that may exhibit elevated temperatures includes junctions between segment hangers or hook structures and the panel, where an increased mass of material at these junctions results in a higher thermal capacitance with resulting retention of heat in the absence of effective cooling.

The present invention provides intermediate impingement plenums that perform plural functions for facilitating controlled cooling of the ring segment. The intermediate plenums are located at the hook-to-panel junctions, with a resulting reduction of thermal mass at these junctions, and a high pressure supply of air is provided from a central plenum to provide impingement cooling. Additionally, the intermediate plenums enable close placement of the convective cooling passages to the inner surface of the panel, and provide a controlled back flow margin through the convective cooling passages with an efficient balance of cooling air flow through leading edge convective cooling passages relative to flow of cooling air through trailing edge convective cooling passages.

FIG. 1 illustrates a portion of a turbine section 10 of a gas turbine engine. Within the turbine section 10 are alternating rows of stationary vanes and rotating blades. In FIG. 1, a single blade 12 forming a row 12 a of blades is illustrated. Also illustrated in FIG. 1 are part of an upstream vane 14 forming a row 14 a of upstream vanes, and part of a downstream vane 16 forming a row 16 a of downstream vanes. The blades 12 are coupled to a disc (not shown) of a rotor assembly. A hot working gas from a combustor (not shown) in the engine flows in a hot gas flow path 20 passing through the turbine section 10. The working gas expands through the turbine 10 as it flows through the hot gas flow path 20 and causes the blades 12, and therefore the rotor assembly, to rotate.

In accordance with an aspect of the invention, an outer seal structure 22 is provided about and adjacent the row 12 a of blades. The seal structure 22 comprises a plurality of ring segments 24, which, when positioned side by side in a circumferential direction of the engine, define the seal structure 22. The seal structure 22 has a ring shape so as to extend circumferentially about its corresponding row 12 a of blades. A corresponding one of the seal structures 22 may be provided about each row of blades provided in the turbine section 10.

The seal structure 22 comprises an inner wall of a turbine housing 25 in which the rotating blade rows are provided and defines sealing structure for preventing or limiting the working gas from passing through the inner wall and reaching other structure of the turbine housing, such as a blade ring carrier 26 and an associated annular cooling fluid plenum 28. It is noted that the terms “inner”, “outer”, “radial”, “axial”, “circumferential”, and the like, as used herein, are not intended to be limiting with regard to orientation of the elements recited for the present invention.

Referring to FIGS. 1 and 2, a single one of the ring segments 24 of the seal structure 22 is shown, it being understood that the other ring segments 24 of the seal structure 22 are generally identical to the single ring segment 24 shown and described. The ring segment 24 comprises a panel 30 including side edges comprising a circumferentially extending leading edge 32, a circumferentially extending trailing edge 34, a first axially extending mating edge 36 (see FIG. 2), and a second axially extending mating edge 38 (see FIG. 2). The panel 30 further includes an outer side 40 (see FIG. 1) and an inner side 42 (see FIG. 1), wherein the inner side 42 comprises a radially inner side and defines a corresponding portion of the hot gas flow path 20.

The panel 30 defines a structural body for the ring segment 24, and includes one or more front hangers or hook structures 44 and one or more rear hangers or hook structures 45, see FIG. 1. It may be noted that, although the illustrated embodiment shows hook structures for supporting the ring segment 24, the present invention is not necessarily limited to providing support to the panel through hook structures, and other support structures may be implemented in place of the hook structures 44, 45 disclosed herein.

The front hook structure 44 is formed by a front leg portion 44 a supporting a front flange portion 44 b. The rear hook structure 45 is formed by a rear leg portion 45 a supporting a rear flange portion 45 b. As seen in FIG. 3, the front and rear hook structures 44, 45 are rigidly attached to the panel 30 at respective junctions 44 c, 45 c between the leg portions 44 a, 45 a and the outer side 40 of the panel 30, such as via an integral casting. Alternatively, the hook structures 44, 45, or other support structure, may be formed separately and subsequently rigidly attached to the panel 30. Moreover, if formed separately from the panel 30 the hook structures 44, 45, or other support structure, may be formed of the same material or a different material than the panel 30. Each ring segment 24 is mounted within the turbine section 10 via the front hook structures 44 engaging a corresponding structure 46 of the blade ring carrier 26, and the rear hook structures 45 engaging a corresponding structure 48 of the blade ring carrier 26, as seen in FIG. 1.

Referring to FIG. 1, the blade ring carrier 26 defines, in cooperation with an impingement plate 50, also known as an impingement plate, the annular cooling fluid plenum 28, which defines a source of cooling fluid for the seal structure 22, as is described further below. The impingement plate 50 is secured to the blade carrier ring 26 at fore and aft locations 52, 54 to form an impingement cavity 55 between the impingement plate 50 and the panel 30, as shown in FIG. 1. The cooling fluid plenum 28 receives cooling fluid through a channel 56 formed in the blade ring carrier 26 from a source of cooling fluid, such as bleed air from a compressor (not shown) of the gas turbine engine. As shown in FIG. 1, the impingement plate 50 includes a plurality of impingement holes 58 therein. Cooling fluid in the cooling fluid plenum 28 flows through the impingement holes 58 in the impingement plate 50 and impinges on the outer side 40 of the panel 30 during operation of the engine.

Referring to FIGS. 1 and 2, the outer side 40 of the illustrated panel 30 is formed with a central recessed portion or impingement bay 60 defining a recessed surface 60 a of the panel 30. The outer side 40 of the panel 30 further comprises a rim portion 62 surrounding the impingement bay 60. The rim portion 62 comprises an unrecessed portion 62 a extending around a periphery of the impingement bay 60 along each of the side edges, i.e., the leading edge 32, the trailing edge 34, the first mating edge 36, and the second mating edge 38. First, second, third, and fourth impingement bay walls 32 a, 34 a, 36 a, 38 a, i.e., corresponding to the leading edge 32, the trailing edge 34, the first mating edge 36, and the second mating edge 38 (see FIG. 2), extend at least partially in the radial direction between the recessed surface 60 a and the unrecessed portion 62 a and define the outer periphery of the impingement bay 60. It should be noted that the outer side 40 of the panel 30 need not comprise the impingement bay 60 and the rim portion 62 and may comprise, for example, an area that is substantially entirely planar.

Referring to FIGS. 2, 2A and 3, the panel 30 comprises a cooling system 64. In accordance with an aspect of the invention, the cooling system 64 comprises elongated front and rear intermediate plenums 66A, 66B extending in the circumferential direction and located radially between the inner side 42 of the panel 30 and respective ones of the front and rear hook structures 44, 45. Specifically, the front intermediate plenum 66A is located at an axial location that is adjacent to the leading edge 32 and, in particular, is located between radially extending lines 44 ₁ and 44 ₂ that are collinear with the axial locations of fore and aft faces 44 _(F) and 44 _(A) of the front hook structure 44 adjacent to their junction with the panel 30. Similarly, the rear intermediate plenum 66B is located at an axial location that is adjacent to the trailing edge 34 and, in particular, is located between radially extending lines 45 ₁ and 45 ₂ that are collinear with the axial locations of fore and aft faces 45 _(F) and 45 _(A) of the rear hook structure 45 adjacent to their junction with the panel 30.

Referring to FIG. 3, a plurality of forward cooling fluid feed passages 68A extend forwardly from the impingement bay 60 to the front intermediate plenum 66A for supplying cooling fluid to the front intermediate plenum 66A. For example, the forward cooling fluid feed passages 68A extend from an inlet end, located at the impingement bay wall 32 a, to the intermediate plenum 66A. A plurality of rearward cooling fluid feed passages 68B extend rearwardly from the impingement bay 60 to the rear intermediate plenum 66B for supplying cooling fluid to the rear intermediate plenum 66B. For example, the rearward cooling fluid feed passages 68B extend from an inlet end, located at the impingement bay wall 34 a, to the intermediate plenum 66B. In addition to supplying cooling fluid to the front and rear intermediate plenums 66A, 66B, the cooling fluid feed passages 68A, 68B also provide convective cooling to the panel 30 in the regions between the impingement bay 60 and the intermediate plenums 66A, 66B.

Referring to FIG. 3, a plurality of front convective cooling passages 70A extend through the panel 30 from the front intermediate plenum 66A to the leading edge 32 for cooling the inner side 42 of the panel 30 in a region extending axially between the hook structure 44 and the leading edge 32. A plurality of rear convective cooling passages 70B extend through the panel 30 from the rear intermediate plenum 66B to the trailing edge 34 for cooling the inner side 42 of the panel 30 in a region extending axially between the hook structure 45 and the trailing edge 34. The intermediate plenums 66A, 66B are located in axial alignment with respective ones of the front and rear hook structures 44, 45 and define an area of reduced thermal mass adjacent to the radially inner ends of hook structures 44, 45, i.e., adjacent to the junctions 44 c, 45 c with the panel 30.

A passage diameter of the convective cooling passages 70A, 70B is less than a diameter of the cooling fluid feed passages 68A, 68B, and the intermediate plenums 66A, 66B each define a diameter greater than both the respective convective cooling passage diameters 70A, 70B and the respective diameters of the cooling fluid feed passages 68A, 68B. In accordance with an aspect of the invention, the cooling fluid feed passages 68A, 68B provide impingement cooling to the intermediate plenums 66A, 66B. It should be noted that, in order to maintain a robust margin over backflow from the gas path pressure back to the intermediate plenums 66A, 66B, a cooling fluid pressure drop through the cooling fluid feed passages 68A, 68B extending to the intermediate plenums 66A, 66B is typically less than a cooling fluid pressure drop through the convective cooling passages 70A, 70B leading from the intermediate plenums 66A, 66B to the leading and trailing edges 32, 34. Further, the passage of air through the cooling fluid feed passages 68A, 68B creates a pressure drop of about 3% between the impingement cavity 55 and the intermediate plenums 66A, 66B in order to produce a relatively high level of impingement cooling within the intermediate plenums 66A, 66B. The impingement cooling provided to the area of the junctions 44 c, 45 c further contributes to convective heat transfer from this area with an associated reduction of temperature. This may be considered beneficial in that, although the portion of the panel 30 defined by the impingement bay 60 may receive adequate cooling for reducing the temperature of the adjacent inner surface 42, the axially adjacent regions of the panel 30 aligned with the hook structures 44, 45 may act as a sink to retain heat. Hence, the reduction of mass resulting from the cavities formed by the intermediate plenums 66A, 66B in combination with increased convective heat transfer through impingement cooling within the hook structure junction areas 44 c, 45 c provides a substantial temperature reduction to this portion of the ring segment 24.

As seen in FIGS. 2, 2A and 3A, the convective cooling passages 70A, 70B extend generally parallel and closely adjacent to the inner side 42 of the panel 30, such that each of the convective cooling passages 70A, 70B are equidistant from the inner surface 42 of the panel 30 from a fluid supply end 70A₁, 70B₁ to a fluid exit end 70A₂, 70B₂. The fluid supply ends 70A₁, 70B₁ are located axially aligned with at least a portion of respective ones of the front and rear hook structures 44, 45, i.e., the fluid supply ends 70A₁, 70B₁ are located between respective radially extending lines 44 ₁, 44 ₂ and 45 ₁, 45 ₂, and the fluid exit ends 70A₂, 70B₂ comprise cooling fluid exit openings at the leading and trailing edges 32, 34. In accordance with an aspect of the invention, the convective cooling passages 70A, 70B are located as close as practically possible to the inner surface 42 of the panel 30. For example, in a preferred embodiment, the close spacing of the convective cooling passages 70A, 70B is defined by the convective cooling passages 70A, 70B being radially spaced within a distance of about one passage diameter D_(C) from the inner surface 42 of the panel 30, as seen in FIG. 3A, such that a substantially low thermal mass of the panel material is between the inner surface 42 and a flow of cooling air passing through the convective cooling passages 70A, 70B.

The thermal efficiency of the present cooling system is increased by providing a reduced diameter for the convective cooling passages 70A, 70B with a resulting increase in convective cooling passage heat transfer. The convective cooling passage heat transfer is proportional to (1/D_(C))^(1.2), accounting for a convective cooling passage surface area increase, which is proportional to (1/D_(C)), and an internal heat transfer coefficient increase, which is proportional to (1/D_(C))^(0.2).

It should be noted that the intermediate plenums 66A, 66B facilitate placement of the convective cooling passages 70A, 70B in close proximity to the inner surface 42 of the panel 30. In particular, the intermediate plenums 66A, 66B comprise cylindrical passages that provide an interface between the cooling fluid feed passages 68A, 68B and the convective cooling passages 70A, 70B wherein the circumference of the intermediate plenums 66A, 66B includes respective radially innermost sectors 66A_(S), 66B_(S) located closely adjacent to the inner surface 42. The sectors 66A_(s), 66B_(s) provide a connection point, connecting to the convective cooling passages 70A, 70B at locations generally tangential to the cylindrical walls of the intermediate plenums 66A, 66B, at the lower half of the intermediate plenums 66A, 66B, and facilitating the placement of the convective cooling passages 70A, 70B in close proximity to the inner surface 42 of the panel 30.

The intermediate plenums 66A, 66B further facilitate close placement, within machine limits, of the convective cooling passages 70A, 70B adjacent to each other along their length from the location of the hook structures, i.e., between the radial lines 44 ₁, 44 ₂ and 45 ₁, 45 ₂, to the leading and trailing edges 32, 34, respectively. The intermediate plenums 66A, 66B extend substantially the entire circumferential extent of the ring segment 24, i.e., beyond the circumferential bounds of the impingement bay 60 defined by the impingement bay walls 36 a, 38 a. In particular, the impingement plenums 66A, 66B include respective ends 66A_(E1), 66A_(E2) and 66B_(E1), 66B_(E2) that are located close to elongated axial plenum structures 72A, 72B that extend in the axial direction parallel and adjacent to the first and second mating edges 36, 38. The convective cooling passages 70A, 70B extend parallel to the mating edges 36, 38 in side-by-side relation to each other in a circumferentially extending plane. Further, the convective cooling passages 70A, 70B extend axially from the intermediate plenums 66A, 66B at locations adjacent to the ends 66A_(E1), 66A_(E2) and 66B_(E1), 66B_(E2) not circumferentially aligned with any of the cooling fluid feed passages 68A, 68B, such as may be required in order to permit space for passages providing cooling fluid to the axial plenum structures 72A, 72B. Hence, it may be understood that a relatively high density of the convective cooling passages 70A, 70B is provided in the area bounded between the axial plenum structures 72A, 72B, as well as between the intermediate plenums 66A, 66B and the respective leading and trailing edges 32, 34, to provide a high thermal efficiency cooling system 64.

As noted above, the pressure drop of the cooling fluid feed passages 68A, 68B leading to the intermediate plenums 66A, 66B is different from the pressure drop of the convective cooling passages 70A, 70B. The intermediate plenums 66A, 66B facilitate adjusting the pressure of the cooling air to the convective cooling passages 70A, 70B independently of the pressure of the impingement air provided for cooling at the impingement bay 60 and independent of each other. In particular, the cooling requirements and pressure adjacent the leading edge 32 of the panel 30 may typically be greater than the cooling requirements and pressure adjacent the trailing edge 34, such that the forward cooling fluid feed passages 68A may, for example, be sized larger than the rearward cooling fluid feed passages 68B in order for the front intermediate plenum 66A to be provided with a relatively higher pressure than the rear intermediate plenum 66B. By limiting the size of the rearward cooling fluid feed passages 68B to only provide an amount of cooling air necessary for cooling the trailing edge portion of the panel 30, energy losses associated with cooling the ring segments 24 may be minimized or limited while enabling sufficient cooling to meet the particular cooling needs at the respective leading and trailing edge portions of the panel 30.

Referring to FIGS. 2, 2A and 4, the axial plenum structures 72A, 72B define intermediate plenum structures located in the panel 30 between the impingement bay 60 and respective first and second mating edges 36, 38. A plurality of cooling fluid feed passages 76A, 76B extend from the impingement bay 60 to the respective axial plenum structures 72A, 72B for supplying cooling fluid to the axial plenum structures 72A, 72B. For example, the cooling fluid feed passages 76A, 76B extend from openings in the respective impingement bay walls 36 a, 38 a to the axial plenum structures 72A, 72B. In addition to supplying cooling fluid to the axial plenum structures 72A, 72B, the cooling fluid feed passages 76A, 76B also provide convective cooling to the panel 30 in the regions between the impingement bay 60 and the axial plenum structures 72A, 72B.

A plurality of exit passages 78A, 78B extend from the axial plenum structures 72A, 72B to respective ones of the first and second mating edges 36, 38. The exit passages 78A, 78B may be sized to have a diameter similar to the diameter of the convective cooling passages 70A, 70B, and are sized smaller than the cooling fluid feed passages 76A, 76B, and provide a flow of cooling fluid to the mating edges 36, 38 in addition to providing convective cooling to the panel 30 adjacent to the mating edges 36, 38. Further, the axial plenum structures 72A, 72B may be cylindrical structures that have a diameter greater than both the cooling fluid feed passages 76A, 76B and the exit passages 78A, 78B.

In accordance with an aspect of the invention, the axial plenum structure 72A includes fore and aft axial plenums 72A₁, 72A₂, where the fore axial plenum 72A₁ may extend from a location closely adjacent to the leading edge 32 to a location at approximately mid-way between the leading and trailing edges 32, 34, and the aft axial plenum 72A₂ may extend from a location closely adjacent to the trailing edge 34 to a location at approximately mid-way between the leading and trailing edges 32, 34. The fore and aft axial plenums 72A₁, 72A₂ are formed as separate plenums, i.e., not in direct fluid communication with each other. Similarly, the axial plenum structure 72B includes fore and aft axial plenums 72B₁, 72B₂, where the fore axial plenum 72B₁ may extend from a location closely adjacent to the leading edge 32 to a location at approximately mid-way between the leading and trailing edges 32, 34, and the aft axial plenum 72B₂ may extend from a location closely adjacent to the trailing edge 34 to a location at approximately mid-way between the leading and trailing edges 32, 34. The fore and aft axial plenums 72B₁, 72B₂ are formed as separate plenums, i.e., not in direct fluid communication with each other. The separate fore and aft axial plenums 72A₁, 72A₂ and 72B₁, 72B₂ permit different fluid flows and or pressures to be provided to the different axial plenums, and enable fine tuning of the cooling along the mating edges 36, 38.

In addition, although the illustrated embodiment shows the intermediate plenums 66A, 66B as separate from the axial plenum structures 72A, 72B, the length of the intermediate plenum 66A may be extended to be n fluid communication with connected to one or both of the axial plenum structures 72A, 72B, e.g., may be connected to one or both of the axial plenums 72A₁, 72B₁. Similarly, the intermediate plenum 66B may be extended to be n fluid communication with one or both of the axial plenum structures 72A, 72B, e.g., may be connected to one or both of the axial plenums 72A₂, 72B₂. The described connection(s) between the intermediate plenums 66A, 66B and the axial plenum structures 72A, 72B may be provided to enable a controlled backflow margin to compensate for machining tolerances of the various cooling passages 70A, 70B, 78A, 78B.

While particular embodiments of the present invention have been illustrated and described, it would be obvious to those skilled in the art that various other changes and modifications can be made without departing from the spirit and scope of the invention. It is therefore intended to cover in the appended claims all such changes and modifications that are within the scope of this invention. 

What is claimed is:
 1. A ring segment for a gas turbine engine comprising: a panel comprising: a plurality of side edges including leading and trailing edges extending in a circumferential direction, and first and second mating edges extending in an axial direction; an outer side and an inner side, wherein cooling fluid is provided to said outer side and said inner side defines at least a portion of a hot gas flow path through the gas turbine engine; and a central recessed portion defining a recessed surface formed in said outer side and surrounded by a rim portion comprising an unrecessed portion extending around an outer periphery of said recessed portion along each of said side edges; a front hook structure extending in a radial direction from said rim portion at a leading edge side of said recessed portion; a rear hook structure extending in a radial direction from said rim portion at a trailing edge side of said recessed portion; a cooling system within said panel that receives cooling fluid from said outer side of said panel for cooling said panel, said cooling system comprising: an elongated intermediate plenum extending in the circumferential direction and located radially between said inner side of said panel and one of said front and rear support structures; a plurality of cooling fluid feed passages extending from said recessed portion to said intermediate plenum for supplying cooling fluid to said intermediate plenum; a plurality of convective cooling passages extending through said panel from said intermediate plenum to one of said leading and trailing edges for cooling said inner side of said panel; and said intermediate plenum being located in axial alignment with said one of said front and rear support structures and defining an area of reduced thermal mass adjacent to a radially inner end of said one of said front and rear support structures.
 2. The ring segment of claim 1, wherein said cooling fluid feed passages provide impingement cooling to said intermediate plenum.
 3. The ring segment of claim 2, wherein a cooling fluid pressure drop through said feed passages is less than a cooling fluid pressure drop through said convective cooling passages.
 4. The ring segment of claim 3, wherein a passage diameter of said convective cooling passages is less than a diameter of said cooling fluid feed passages, and said intermediate plenum defines a diameter greater than both said convective cooling passage diameter and said diameter of said cooling fluid feed passages.
 5. The ring segment of claim 1, wherein fluid supply ends of said convective cooling passages are located at said intermediate plenum and said fluid supply ends are axially aligned with at least a portion of said one of said front and rear support structures.
 6. The ring segment of claim 1, wherein said cooling structure further includes: an elongated axial plenum structure extending in the axial direction; a plurality of cooling fluid feed passages extending from said recessed portion to said axial plenum structure for supplying cooling fluid to said axial plenum structure; and a plurality of exit passages extending from said axial plenum structure to at least one of said first and second mating edges.
 7. The ring segment of claim 6, wherein said axial plenum structure comprises a forward plenum and a rearward plenum, and cooling fluid is supplied to said forward plenum at a different flow rate than cooling fluid supplied to said rearward plenum.
 8. The ring segment of claim 6, wherein said axial plenum structure includes first and second axial plenum structures extending in the axial direction adjacent to said first and second mating edges, respectively, and said intermediate plenum includes opposing ends located adjacent to said first and second axial plenum structures.
 9. The ring segment of claim 1, wherein said convective cooling passages extend generally parallel to said inner side of said panel and are defined by a passage diameter, and said convective cooling passages are spaced within a distance of about one passage diameter from said inner side of said panel.
 10. The ring segment of claim 9, wherein said passage diameter of said convective cooling passages is less than a diameter of said cooling fluid feed passages.
 11. The ring segment of claim 1, wherein said intermediate plenum is a first intermediate plenum located in axial alignment with said front hook structure, said cooling system further including: a second elongated intermediate plenum extending in the circumferential direction and located in axial alignment with said rear hook structure; a plurality of cooling fluid feed passages extending from said recessed portion to said second intermediate plenum for supplying cooling fluid to said second intermediate plenum; a plurality of convective cooling passages extending through said panel from said second intermediate plenum to said trailing edge for cooling said inner side of said panel.
 12. A ring segment for a gas turbine engine comprising: a panel comprising a plurality of side edges including leading and trailing edges extending in a circumferential direction, and first and second mating edges extending in an axial direction, said panel further comprising an outer side and an inner side, wherein cooling fluid is provided to said outer side and said inner side defines at least a portion of a hot gas flow path through the gas turbine engine; front and rear support structures extending in a radial direction from said outer side of said panel; a cooling system within said panel that receives cooling fluid from said outer side of said panel for cooling said panel, said cooling system comprising: first and second elongated intermediate plenums extending in the circumferential direction and located radially between said inner side of said panel and respective ones of said front and rear support structures; a plurality of cooling fluid feed passages extending from said outer side of said panel to said intermediate plenums for supplying cooling fluid to said intermediate plenums; a plurality of convective cooling passages extending through said panel from said first and second intermediate plenums to said leading and trailing edges, respectively, for cooling said inner side of said panel; said first and second intermediate plenums being located in axial alignment with said front and rear support structures, respectively, and defining an area of reduced thermal mass adjacent to a radially inner end of each of said front and rear support structures.
 13. The ring segment of claim 12, wherein said convective cooling passages define a passage diameter that is less than a diameter of said cooling fluid feed passages, and said first and second intermediate plenums define a diameter greater than both said passage diameter and said diameter of said cooling fluid feed passages.
 14. The ring segment of claim 12, wherein fluid supply ends of said convective cooling passages are located at said first and second intermediate plenums, and said fluid supply ends are axially aligned with at least a portion of respective ones of said front and rear support structures.
 15. The ring segment of claim 12, wherein said cooling structure further includes: first and second elongated axial plenum structures extending in the axial direction adjacent to said first and second mating edges, respectively; a plurality of cooling fluid feed passages extending from said outer side of said panel to said axial plenum structures for supplying cooling fluid to said axial plenum structures; and a plurality of exit passages extending from said axial plenum structures to one of said first and second mating edges.
 16. The ring segment of claim 15, wherein each of said first and second axial plenum structures comprises a forward plenum and a rearward plenum, and cooling fluid is supplied to said forward plenums at a different flow rate than cooling fluid supplied to said rearward plenums.
 17. The ring segment of claim 15, including a fluid connection between ends of each of said first and second intermediate plenums and said first and second axial plenum structures.
 18. A ring segment for a gas turbine engine comprising: a panel comprising a plurality of side edges including leading and trailing edges extending in a circumferential direction, and first and second mating edges extending in an axial direction, said panel further comprising an outer side and an inner side, wherein cooling fluid is provided to said outer side and said inner side defines at least a portion of a hot gas flow path through the gas turbine engine; a cooling system within said panel that receives cooling fluid from said outer side of said panel for cooling said panel, said cooling system comprising: an elongated intermediate plenum extending in the circumferential direction and located radially between said inner and outer sides of said panel; a plurality of cooling fluid feed passages extending from said outer side of said panel to said intermediate plenum for supplying cooling fluid to said intermediate plenums; a plurality of convective cooling passages extending through said panel from said intermediate plenum to one of said leading and trailing edges for cooling said inner side of said panel; and said convective cooling passages extend axially generally parallel to said inner side of said panel and are defined by a passage diameter, and said convective cooling passages are spaced within a distance of about one passage diameter from said inner side of said panel.
 19. The ring segment of claim 18, wherein said intermediate plenum is aligned in the axial direction with a radially inner end of a hook structure that extends in a radial direction outwardly from said outer side of said panel for supporting said panel within the engine, said intermediate plenum effecting an area of reduced thermal mass adjacent to said inner end of said hook structure.
 20. The ring segment of claim 18, wherein said passage diameter of said convective cooling passages is less than a diameter of said cooling fluid feed passages, and said intermediate plenum defines a diameter greater than both said convective cooling passage diameter and said diameter of said cooling fluid feed passages. 